Didier Stevens is an IT Security Consultant currently working at a large Belgian financial corporation. He is employed by Contraste Europe NV, an IT Consulting Services company (http://www.contraste.com). You can find his open source security tools on his IT security related blog at http://blog.DidierStevens.com.
Didier has released several tools and techniques (open source and public domain) for users to protect their machines against malware and to deal with the results of a malware infection.